Catheter having a readily bondable multilayer soft tip

ABSTRACT

A balloon catheter having a soft distal tip member having a non-tacky inner (liner) layer material and a soft flexible outer layer material, with both materials being readily thermally bondable to the catheter balloon.

CROSS-REFERENCES TO RELATED APPLICATIONS

None

BACKGROUND OF THE INVENTION

This invention relates generally to catheters, and particularlyintravascular catheters for use in percutaneous transluminal coronaryangioplasty (PTCA) or for the delivery of stents.

In percutaneous transluminal coronary angioplasty (PTCA) procedures aguiding catheter is advanced in the patient's vasculature until thedistal tip of the guiding catheter is seated in the ostium of a desiredcoronary artery. A guidewire is first advanced out of the distal end ofthe guiding catheter into the patient's coronary artery until the distalend of the guidewire crosses a lesion to be dilated. A dilatationcatheter, having an inflatable balloon on the distal portion thereof, isadvanced into the patient's coronary anatomy over the previouslyintroduced guidewire until the balloon of the dilatation catheter isproperly positioned across the lesion. Once properly positioned, thedilatation balloon is inflated with inflation fluid one or more times toa predetermined size at relatively high pressures so that the stenosisis compressed against the arterial wall to open up the vascularpassageway. Generally, the inflated diameter of the balloon isapproximately the same diameter as the native diameter of the body lumenbeing dilated so as to complete the dilatation but not overexpand theartery wall. After the balloon is finally deflated, blood flow resumesthrough the dilated artery and the dilatation catheter and the guidewirecan be removed therefrom.

In such angioplasty procedures, there may be restenosis of the artery,i.e. reformation of the arterial blockage, which necessitates eitheranother angioplasty procedure, or some other method of repairing orstrengthening the dilated area. To reduce the restenosis rate ofangioplasty alone and to strengthen the dilated area, physicians nownormally implant an intravascular prosthesis, generally called a stent,inside the artery at the site of the lesion. Stents may also be used torepair vessels having an intimal flap or dissection or to generallystrengthen a weakened section of a vessel or to maintain its patency.Stents are usually delivered to a desired location within a coronaryartery in a contracted condition on a balloon of a catheter which issimilar in many respects to a balloon angioplasty catheter, and expandedwithin the patient's artery to a larger diameter by expansion of theballoon. The balloon is deflated to remove the catheter and the stentleft in place within the artery at the site of the dilated lesion. Seefor example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No.5,458,615 (Klemm et al.), which are incorporated herein by reference.

An essential step in effectively performing a PTCA procedure is properlypositioning the balloon catheter at a desired location within thecoronary artery. To properly position the balloon at the stenosedregion, the catheter shaft must be able to transmit force along thelength of the catheter shaft to allow it to be pushed through thevasculature. However, the catheter shaft must also retain sufficientflexibility to allow it to track over a guidewire through the oftentortuous vasculature. Additionally, the catheter must have goodcrossability (i.e., the ability of the catheter distal end to crossstenosed portions of the vascular anatomy).

Conventional intravascular catheters have commonly included a softdistal tip which prevents or minimizes injury to the vessel duringadvancement of the catheter therein. One difficulty has been thetendency of the soft tip materials to frictionally engage or stick tothe guidewire (commonly referred to as “locking” of the guidewire),making it difficult to advance or retract the catheter. Additionally, inthe design of soft tips, it is necessary to minimize the stiffness ofthe distal end of the catheter to aid in flexibly tracking the deviceduring dilatation and stenting procedures, while nonetheless preventingstructural failure/disengagement of the soft tip or kinking at thejunction between the soft tip and catheter shaft.

Accordingly, it would be a significant advance to provide a catheterwith a soft tip having improved performance. This invention satisfiesthese and other needs.

SUMMARY OF THE INVENTION

The invention is directed to a balloon catheter having a soft distal tipmember having a non-tacky inner (liner) layer material and a softflexible outer layer material, with both materials being readilythermally bondable to the catheter balloon. The tip is fusion bonded tothe distal end of the balloon, in a configuration which preferablyprovides a securely bonded yet flexible and soft distal end with anon-tacky inner surface.

A catheter of the invention generally comprises an elongated cathetershaft, a balloon on a distal shaft section, and a distal tip member at adistal end of the catheter having an inner layer formed of a firstpolymeric material which has a first Shore durometer hardness and whichdefines at least a section of the lumen of the distal tip, and an outerlayer formed of a second polymeric material which has a lower Shoredurometer hardness than the first polymeric material and which is fusionbond compatible with the first polymeric material. More specifically, inone embodiment, the balloon catheter comprises an elongated cathetershaft having a proximal end, a distal end, a proximal shaft section, adistal shaft section, a guidewire receiving lumen extending along atleast a distal portion of the catheter shaft, and an inflation lumen,and an inflatable balloon sealingly secured to the distal shaft sectionso that an interior of the balloon is in fluid communication with theshaft inflation lumen, and a distal tip member (having the inner layerformed of the first polymeric material and the outer layer formed of thesecond polymeric material) which has a proximal end longitudinallyspaced distally apart from the distal end of the elongated cathetershaft with a gap there between, and a lumen which extends to a guidewiredistal port in communication with the shaft guidewire lumen. Theinflatable balloon has a distal skirt section fusion bonded to theproximal end of the tip, such that a proximal section of the tip is afused blend of the balloon distal skirt section and the inner and outerlayers of the tip, the fused blend having both the outer layer materialand inner layer material of the tip fused with the material of thedistal skirt section along at least the proximal section of the tip. Ina presently preferred embodiment, the inflatable balloon is formed atleast in part of the first polymeric material (i.e., the same polymericmaterial as the inner layer of the tip).

The first and second polymeric materials are preferably of the samepolymer family, e.g., polyamides, and more preferably are of the samepolymer type, e.g., a polyether block amide (PEBAX), although it shouldbe understood that the first polymeric material has a different Shoredurometer hardness than the second polymeric material such that thefirst and second polymeric materials are not the same polymericmaterial. In a presently preferred embodiment, the first and secondpolymeric materials are a polyamide such as a polyether block amide(PEBAX) copolymer or a nylon.

The first polymeric material is preferably a relatively high Shoredurometer material providing a non-tacky inner surface along at least asection of the distal tip. For example, relatively high durometerpolyamides are typically non-tacky whereas relatively low durometerpolyamides are tacky (adhesive stickiness), at least at temperaturescommonly encountered during assembly or use of the catheter. Such tackymaterials have an increased risk of adhering to a processing mandrelduring assembly of the catheter, potentially resulting in tearing/damageof the tip. Moreover, during use of the catheter in an interventionalmedical procedure, such tacky materials can cause “locking” of theguidewire, thus disadvantageously affecting deliverability of thecatheter. However, unlike attempts to improve processability anddeliverability of the catheter by having a distal end with an innerlubricious layer of a material such as high density polyethylene (HDPE)or polytetrafluoroethylene (PTFE) and an outer layer of a bondablematerial for heat fusion bonding to the balloon, both the inner andouter layers of the distal tip of the invention are individually heatfusion (i.e., thermally) bondable to the balloon (and do form a heatfusion bond to the balloon). As a result, tip integrity is improved in acatheter of the invention.

A method of making a catheter of the invention generally comprisespositioning a proximal end of a distal tip member in contact with (e.g.,within) a distal skirt section of the balloon and fusion bonding thedistal tip to the distal skirt section, the distal tip member havingcoextruded inner and outer layers extending from the proximal end of thetip, and the inner layer is formed of a first polymeric material whichhas a first Shore durometer hardness, and the outer layer is formed of asecond polymeric material which has a lower Shore durometer hardnessthan the first polymeric material and which is fusion bond compatiblewith the first polymeric material, and the balloon is formed at least inpart of a polymeric material fusion bond compatible with the distal tipmaterials. The fusion bonding typically involves applying heat and aninward force on an outer surface of a distal portion of the balloondistal skirt section to fusion bond an inner surface of the distal skirtsection to the proximal end of the distal tip member, such that aproximal section of the tip is a fused blend of the balloon distal skirtsection and the inner and outer layers of the tip, the fused blendhaving both the outer layer and inner layer of the distal tip fused withthe material of the distal skirt section along the proximal section ofthe tip. The method includes bonding the balloon distal skirt section ofthe elongated catheter shaft, typically by applying heat and a radiallyinward force on an outer surface of a proximal portion of the balloondistal skirt section, located proximal to the fusion bonded distal tipmember, to bond the distal skirt section to the elongated shaft, suchthat the proximal end of the tip is longitudinally spaced distally apartfrom the elongated shaft by a gap there between.

A catheter of the invention has enhanced processability anddeliverability due to the configuration of the multilayered distal tip.The soft distal tip provides a flexible, atraumatic distal end, with anon-tacky inner surface which prevents or inhibits “locking” of theguidewire during an interventional procedure, while nonetheless having ahigh pull strength for improved tip integrity. These and otheradvantages of the invention will become more apparent from the followingdetailed description and exemplary figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational partially in section view of a balloon catheterembodying features of the invention.

FIGS. 2, 3 and 4 are transverse cross sectional views of the ballooncatheter of FIG. 1, taken along lines 2-2, 3-3 and 4-4, respectively.

FIG. 5 a illustrates a method of making a balloon catheter embodyingfeatures of the invention, during the fusion bonding of a distal tipmember to a distal skirt section of the catheter balloon.

FIG. 5 b illustrates the balloon catheter of FIG. 3 a, after the fusionbonding of the distal tip member, during the fusion bonding of thedistal skirt section to a shaft inner tubular member.

FIG. 6 illustrates the distal end of an alternative embodiment of aballoon catheter embodying features of the invention, in which thedistal tip member is butt-joined to the distal skirt section of thecatheter balloon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a stent delivery balloon catheter 10 embodyingfeatures of the invention, generally comprising an elongated cathetershaft 11 having a proximal end 12 (within a strain relief/proximaladapter), a distal end 13, a proximal shaft section, a distal shaftsection, an inflatable balloon 14 on the distal shaft section, and adistal tip 15 at a distal end of the catheter 10. The catheter shaft 11has an inflation lumen 16 and a guidewire lumen 17. In the illustratedembodiment, the catheter 10 is a rapid exchange-type catheter with theguidewire lumen 17 extending along the distal shaft section to aguidewire proximal port 18 spaced distally from the proximal end 12 ofthe catheter shaft. At the proximal end 12, the shaft connects to strainrelief tubing and a proximal adapter 20. The proximal adapter 20 has aport 21 in fluid communication with the inflation lumen 16 of thecatheter shaft 11 and configured for connecting to a fluid source (notshown) for inflating/deflating the balloon 14. The balloon 14 isillustrated in a noninflated configuration in FIG. 1, with a radiallyexpandable stent 19 mounted on the balloon 14. The distal end ofcatheter 10 may be advanced to a desired region of a patient's bodylumen in a conventional manner with the balloon 14 in the low profile,noninflated configuration, and the balloon 14 inflated by directinginflation fluid into the balloon interior to radially expand the balloonand stent, and the balloon deflated for repositioning or removal fromthe body lumen, leaving the stent 19 implanted in the body lumen. Theballoon 14 can be configured to perform a variety of medical procedures.

In the illustrated embodiment, the shaft 11 comprises an outer tubularmember 22 having an inflation lumen 16 therein, and an inner tubularmember 23 defining a guidewire lumen 17 therein configured to slidinglyreceive a guidewire 24. Specifically, the coaxial relationship betweenouter tubular member 22 and inner tubular member 23 defines annularinflation lumen 16, as best shown in FIG. 2 illustrating a transversecross section of the catheter of FIG. 1, taken along line 2-2. Theinflatable balloon 14 has a proximal skirt section 25 sealingly securedto the distal end of outer tubular member 22 and a distal skirt section26 sealingly secured to the distal end of inner tubular member 23, sothat the balloon interior is in fluid communication with inflation lumen16.

The distal tip 15 has a proximal end 30 longitudinally spaced distallyapart from the distal end 13 of the elongated catheter shaft innertubular member 23 with a gap there between, and a lumen 31 which extendsto a guidewire distal port 32 at the distal end of the tip 15. Thedistal tip lumen 31 and guidewire distal port 32 are communication withthe shaft guidewire lumen 17 in the inner tubular member 23, so that theguidewire 24 is slidably disposed therein.

The distal tip 15 has an inner layer 33 formed of a first polymericmaterial which has a first Shore durometer hardness and which defines atleast a section of the lumen 31 of the distal tip 15, and an outer layer34 formed of a second polymeric material which has a lower Shoredurometer hardness than the first polymeric material and which is fusionbond compatible with the first polymeric material. Preferably, theballoon 14 is formed at least in part of the first or the secondpolymeric material. More specifically, in one presently preferredembodiment, the balloon has at least a layer formed of the firstpolymeric material (i.e., of the same polymer material type anddurometer hardness as the inner layer 33 of the distal tip 15). Forexample, in one embodiment, the balloon is a single layered balloonformed of the first polymeric material. However, catheter balloons canconventionally be formed of multiple materials, for example as amultilayered balloon. Thus, in an alternative embodiment, the balloonhas an outer layer formed of the first polymeric material, and an innerlayer formed of a different polymeric material.

In the embodiment of illustrated in FIG. 1, along a proximal section 36of the distal tip 15, the distal tip 15 is fusion bonded to an innersurface of a distal end of the distal skirt section 26, such that theproximal end 30 of the distal tip 15 is surrounded by the distal skirtsection 26. Both the inner layer 33 material and the outer layer 34material of the tip 15 extend along the proximal section 36 of the tip15, such that the proximal section 36 of the tip 15 is a fused blend ofthe balloon distal skirt section 26 and the inner and outer layers 33,34 of the tip 15. Fusion bonding the inner surface of the distal skirtsection 26 to the outer surface of the distal tip 15 causes thematerials to soften or melt, and flow sufficiently such that thematerial of the inner layer 33 comes into contact with and fuses to thematerial of the distal skirt section 26, to form a fused blend of allthree of the inner layer, outer layer, and distal skirt sectionmaterials. Thus, the fused blend has both the outer layer 34 materialand inner layer 33 material of the tip 15 fused to the material of thedistal skirt section 26 along the proximal section 36 of the tip 15. Theterminology “inner layer 33 material” and “outer layer 34 material”should be understood to refer to the fused blend material at theproximal section 36 (which had the inner layer 33 and outer layer 34extending therealong as discrete layers prior to fusion bonding to theballoon distal skirt section 26) which, after the fusion bonding, hasthe material of the inner layer 33 and the material of the outer layer34 within the blended fusion bond without the defined structure of theoriginal discrete layers.

The inner layer 33 material and the outer layer 34 material both extendto the proximal end 30 of the distal tip 15. Thus, the fused blend ofall three materials (the inner layer 33 material, the outer layer 34material, and the distal skirt section 26 material) extends along theentire length of the portion of the distal skirt section fusion bondedto the distal tip 15.

A distal section of the distal tip member 15 is located distal to thefused proximal section 36 of the tip 15 and balloon distal skirt section26. Thus, a distal end 27 of the balloon distal skirt section 26 isproximally spaced from the distal end of the distal tip 15. FIG. 3illustrates a transverse cross section along line 3-3 in FIG. 1 throughthe fused proximal section 36, and FIG. 4 illustrates a transverse crosssection along line 4-4 in FIG. 1 through the distal section of the tip15. In a presently preferred embodiment, the distal section of the tip15 is longer than the fused proximal section 36 of the tip. For example,in one embodiment the fused proximal section 36 is about 10% to about25% of the total length of the distal tip 15.

In the embodiment illustrated in FIG. 1, the inner layer 33 and theouter layer 34 of the distal tip 15 form a lap joint to an inner surfaceof the distal skirt section 26, as opposed to a butt joint to the distalskirt section 26. As a result, at least a proximal portion of theballoon distal skirt section 26 surrounds the tip 15 and typically has alarger outer diameter than the distal section of the distal tip 15.Although the distal end 27 of the distal skirt section 26 is illustratedwith a sharply squared surface in FIG. 1, it should be understood thatit typically has a rounded and tapered outer surface after being bondedto the underlying distal tip 15. FIG. 6 illustrates an alternativeembodiment, in which the proximal end of the distal tip 15 is buttjoined to the distal end of the distal skirt section 26. The polymericmaterials and fusion bonding are otherwise the same as the embodiment ofFIG. 1, such that the embodiment of FIG. 6 similarly has the fusedproximal section 36 formed of a fused blend of the balloon distal skirtsection 26 and the inner and outer layers 33, 34 of the tip 15.

The Shore durometer hardness of the first polymeric material (i.e.,inner layer 33 of the distal tip 15 and the balloon 14) is generallyabout 63 D to about 75 D, whereas the Shore durometer hardness of thesecond polymeric material (i.e., outer layer 34 of the distal tip 15) isgenerally about 40 D to about 60 D. In a presently preferred embodiment,the first and second polymeric materials are a polyether block amidecopolymer (PEBAX). More specifically, in one embodiment, the firstpolymeric material is a PEBAX 72 D and the second polymeric material isa PEBAX 55 D. The relatively high durometer material, PEBAX 72 D, is apresently preferred material for the inner layer 33 of the distal tip15. However, a lower durometer (softer) material such as PEBAX 63 D canalternatively be used for the inner layer 33, but is less preferred dueat least in part to the lower pull strength of the resulting distal tip,and the generally higher frictional force (or tackiness) of the softermaterial.

The lower durometer of the second polymeric material provides softnessto the distal tip 15, and thus the outer layer 34 of the distal tip 15typically has a relatively low flexural modulus of not greater thanabout 50,000 psi at room temperature. The distal tip must be flexibleand soft enough to be atraumatic and allow for tracking the catheter ona guidewire in the patient's vessels during a medical procedure. Thedistal tip 15 is typically softer and more flexible than the portion ofthe shaft (e.g., the inner tubular member 23) proximally adjacent to thedistal tip which defines the guidewire lumen 17 in communication withthe distal tip lumen 31. In one embodiment, the proximally adjacentportion of the shaft (e.g., inner tubular member 23) has an outer layerwith a higher flexural modulus than the outer layer 34 of the distal tip15. The configuration of the distal end of the catheter 10 at the distaltip 15 preferably provides a highly flexible distal end with an improvedflexibility transition, while nonetheless providing a high pull strengthdistal tip with a non-tacky inner surface as discussed herein.

The distal tip 15 is typically formed by coextruding the inner and outerlayers 33, 34 together. Preferably, the inner layer is at most about 50%of the thickness of the tip, i.e., along the distal section of the tip15 where the inner layer 33 and outer layer 34 remain as discrete layersafter the tip 15 is fusion bonded along the proximal section 36. Morespecifically, the inner layer 33 thickness is typically about equal toor about 20% thinner than the outer layer 34 of the distal tip 15. As aresult, there is a sufficient amount of the relatively high durometerfirst material present to provide a desired high tip pull strength. Inone embodiment, the tip pull strength is about 0.8 to about 2.5 lbs, andmore preferably is about 1 to about 2 lbs. Moreover, although thematerials blend along the fused proximal section 36 of the tip, asufficient amount of the (non-tacky) relatively high durometer firstmaterial is present in the blend to provide an inner surface which doesnot produce disadvantageous adhering of surfaces, such as the guidewire,thereto.

Although the first polymeric material is non-tacky at body temperature,the first polymeric material is not a lubricious polymeric material(e.g., the non-lubricious first polymeric material has a staticcoefficient of friction of greater than about 0.35). However, the distaltip 15 forms a relatively short section of the guidewire lumen 17, andthe inner surface of the inner tubular member 23 defining the guidewirelumen 17 proximal to the tip 15 is preferably formed of a lubriciouspolymeric material which facilitates sliding the guidewire within theguidewire lumen 17. The distal tip 15 typically has a length of about 3mm to about 7 mm, or about 1% to about 2.5% of the total length of theguidewire lumen 17 for a rapid exchange type catheter or about 0.2% toabout 0.4% of the total length the catheter. In a presently preferredembodiment, the inner and outer layers 33, 34 of the tip 15 areapproximately equal in length (i.e., equal within normal manufacturingtolerances).

FIGS. 5 a and 5 b illustrate a method of making a balloon catheter witha distal tip embodying features of the invention. The correspondingreference numerals from the embodiment of FIG. 1 are used in FIGS. 5 aand 5 b, but with the reference numerals 15′ and 26′ indicating thedistal tip and balloon distal skirt section, respectively, prior tobeing fusion bonded together in FIG. 5 a. Specifically, FIG. 5 aillustrates a multilayered distal tip member 15′ positioned within adistal skirt section 26′ of the balloon 14, to form a lap joint. Thedistal tip member 15′ has coextruded inner and outer layers 33, 34extending from the proximal to the distal end of the tip 15′ andsurrounded by the distal skirt section 26′ of the balloon 14. Inaccordance with the invention, the inner layer 33 is formed of a firstpolymeric material which has a first Shore durometer hardness, and theouter layer 34 is formed of a second polymeric material which has alower Shore durometer hardness than the first polymeric material andwhich is fusion bond compatible with the first polymeric material, andthe balloon 14 is formed of a polymeric material fusion bond compatiblewith both the first and second polymeric materials. In a presentlypreferred embodiment, the balloon is formed at least in part of thefirst polymeric material.

A tapered mandrel 40 within the lumen 31 of the distal tip 15 keeps thelumen 31 open during fusion bonding of the distal tip to the balloondistal skirt section and facilitates forming the bond between the distaltip 15 and balloon skirt section 26. In a presently preferredembodiment, the process of fusion bonding the distal skirt section 26 tothe distal tip member 15 is separate from the process which fusion bondsthe distal skirt section 26 to the shaft inner tubular member 23.Specifically, the distal skirt section 26 is preferably fusion bondedfirst to the distal tip member 15, and is thereafter fusion bonded tothe shaft inner tubular member 23. Alternatively, the distal skirtsection 26 can be fusion bonded first to the shaft inner tubular member23, or simultaneously fusion bonded to the distal tip and shaft innertubular member.

The method includes applying heat and a radially inward force (indicatedby arrows in the figures) on an outer surface of a distal portion of theballoon distal skirt section 26′, which fusion bonds an inner surface ofthe distal skirt section to the outer surface of the distal tip member15′ in the embodiment of FIG. 5 a. A heat shrink sheath 41 is on thedistal portion of the distal skirt section 26′ during fusion bonding tothe tip 15′. The heat shrink sheath 41 shrinks when heated, to apply theinward force pressing the distal skirt section 26′ against the distaltip 15′. The heat shrink sheath 41 is removed and discarded after thefusion bonding is completed. As discussed above, the resulting fusionbonded proximal section 36 of the tip 15 is a fused blend of the balloondistal skirt section and the inner and outer layers of the tip, and thefused blend has both the outer layer and inner layer of the distal tipfused with the material of the distal skirt section 26 along theproximal section 36 of the tip.

The heat applied during fusion bonding of the distal tip is not lessthan the glass transition temperature of the first polymeric material,and the heat and force are sufficient to cause the polymeric materialsof the inner and outer layers of the tip to melt or flow along theproximal section thereof. Although the outer surface of the inner layer33 was separated from the inner surface of the balloon distal skirtsection by the outer layer 34 prior to the fusion bonding, the materialsare compatible and soften or melt and flow sufficiently such that theinner layer material contacts and fusion bonds to the distal skirtsection material in the resulting blend along fused section 36.

The method includes bonding (e.g., adhesively and/or fusion bonding) theballoon distal skirt section to the elongated shaft 11 (e.g., innertubular member 23). Preferably, the bonding comprises applying heat anda radially inward force on an outer surface of a proximal portion of theballoon distal skirt section 26 (see FIG. 5 b), to thermally bond thedistal skirt section to the elongated shaft inner tubular member 23. Ina presently preferred embodiment, the distal skirt section is fusionbonded to the elongated shaft 11 without an adhesive there between,although in an alternative embodiment an adhesive may be providedbetween the mating surfaces of the inner tubular member and distal skirtsection to strengthen the bond. In FIG. 5 b, a heat shrink sheath 42similar to sheath 41 of FIG. 5 a applies a radially inward force on theproximal portion of the distal skirt section 26 during bonding to theshaft inner tubular member 23, and is thereafter removed along withmandrel 44, leaving the distal skirt section 26 bonded to the innertubular member 23. As discussed above, in one embodiment, the bonding ofthe shaft inner tubular member 23 to the balloon distal skirt section 26occurs after the distal skirt section 26 has been fusion bonded to thedistal tip 15, and as a result, the proximal portion of the balloondistal skirt section is located proximal to the (already) fusion bondeddistal tip member 15. The heat and radially inward force is applied tothe proximal and distal portions of the distal skirt section 26 but ispreferably not focused onto the portion there between which extends overthe gap between the inner tubular member 23 and distal tip member 15. Inthe embodiment illustrated in FIG. 1, the resulting balloon catheter hasthe distal end of the inner tubular member 23 and the proximal end ofthe distal tip 15 spaced apart by a gap there between which is notcompletely filled up by polymeric material caused to soften and flowduring the bonding process.

The dimensions of catheter 10 are determined largely by the size of theballoon and guidewire to be employed, the catheter type, and the size ofthe artery or other body lumen through which the catheter must pass orthe size of the stent being delivered. Typically, the outer tubularmember 22 has an outer diameter of about 0.025 to about 0.04 inch (0.064to 0.10 cm), usually about 0.037 inch (0.094 cm), and the wall thicknessof the outer tubular member 22 can vary from about 0.002 to about 0.008inch (0.0051 to 0.02 cm), typically about 0.003 to 0.005 inch (0.0076 to0.013 cm). The inner tubular member 23 typically has an inner diameterof about 0.01 to about 0.018 inch (0.025 to 0.046 cm), usually about0.016 inch (0.04 cm), and a wall thickness of about 0.004 to about 0.008inch (0.01 to 0.02 cm). The overall length of the catheter 10 may rangefrom about 100 to about 150 cm, and is typically about 143 cm.Preferably, balloon 14 has a length about 0.8 cm to about 6 cm, and aninflated working diameter of about 2 to about 10 mm.

Inner tubular member 23 and outer tubular member 22 can be formed byconventional techniques, for example by extruding and necking materialsalready found useful in intravascular catheters such a polyethylene,polyvinyl chloride, polyesters, polyamides, polyimides, polyurethanes,and composite materials. The various components may be joined usingconventional bonding methods such as by fusion bonding or use ofadhesives. The inner tubular member 23 and outer tubular member 22 aretypically multilayered tubing, or sections of tubing joined end-to-end,as is conventionally known for balloon catheter shafts. Although theshaft is illustrated as having an inner and outer tubular member, avariety of suitable shaft configurations may be used including a duallumen extruded shaft having a side-by-side lumens extruded therein.Additionally, the outer tubular member 23 typically includes supportingmembers including a high strength member such as a hypotube in theproximal shaft section and/or across the guidewire proximal port 18 (notshown). Similarly, although the embodiment illustrated in FIG. 1 is arapid exchange catheter, in one embodiment (not shown) the catheter ofthis invention is an over-the-wire type balloon catheter having theguidewire lumen extending from the guidewire distal port at the catheterdistal end to a guidewire proximal port at the proximal end of thecatheter.

While the present invention is described herein in terms of certainpreferred embodiments, those skilled in the art will recognize thatvarious modifications and improvements may be made to the inventionwithout departing from the scope thereof. For example, althoughdiscussed in terms of an embodiment in which the distal tip member 15 isfusion bonded to the balloon distal skirt section 26, in one embodimentan outer sheath member in place of the balloon distal skirt sectionforms the fusion bond to at least the proximal portion of the distal tipmember, with the outer sheath member extending distally from the distalend of a balloon distal skirt section and preferably being formed of thefirst polymeric material. Moreover, although individual features of oneembodiment of the invention may be discussed herein or shown in thedrawings of the one embodiment and not in other embodiments, it shouldbe apparent that individual features of one embodiment may be combinedwith one or more features of another embodiment or features from aplurality of embodiments.

1. A balloon catheter, comprising: a) an elongated catheter shaft havinga proximal end, a distal end, a proximal shaft section, a distal shaftsection, a guidewire receiving lumen extending along at least a distalportion of the catheter shaft, and an inflation lumen; b) a distal tipmember located at a distal end of the catheter, having a proximal endlongitudinally spaced distally apart from the distal end of theelongated catheter shaft with a gap there between, and a lumen whichextends to a guidewire distal port in communication with the shaftguidewire lumen, and having an inner layer formed of a first polymericmaterial which has a first Shore durometer hardness and which defines atleast a section of the lumen of the distal tip, and an outer layerformed of a second polymeric material which has a lower Shore durometerhardness than the first polymeric material and which is fusion bondcompatible with the first polymeric material; and c) an inflatableballoon sealingly secured to the distal shaft section so that aninterior of the balloon is in fluid communication with the shaftinflation lumen, formed at least in part of a polymeric material fusionbond compatible with the first and second polymeric materials of thetip, and having a distal skirt section surrounding and fusion bonded toa proximal section of the tip along which both the inner and outer layermaterials of the tip extend, such that the proximal section of the tipis a fused blend of the balloon distal skirt section and the inner andouter layers of the tip, the fused blend having both the outer layermaterial and inner layer material of the tip fused to the material ofthe distal skirt section along the proximal section of the tip.
 2. Theballoon catheter of claim 1 wherein the distal tip member has a distalsection located distal to the fused proximal section of the tip andballoon distal skirt section, such that the balloon distal skirt sectionsurrounds the proximal fused section and not the distal section of thetip.
 3. The balloon catheter of claim 2 wherein the inner layer of thetip along the distal section of the tip, located distal to the fusedproximal section of the tip, has a thickness which is about 30% to about50% of the total thickness of the tip along the distal section of thetip.
 4. The balloon catheter of claim 2 wherein the distal section ofthe tip is longer than the fused proximal section of the tip.
 5. Theballoon catheter of claim 1 wherein the inner and outer layers of thetip are approximately equal in length.
 6. The balloon catheter of claim1 wherein the tip has a pull strength of about 0.5 to about 2.5 lbs. 7.The balloon catheter of claim 1 wherein the balloon is formed at leastin part of the first polymeric material.
 8. The balloon catheter ofclaim 1 wherein the balloon is a single-layer balloon formed of thefirst polymeric material.
 9. The balloon catheter of claim 1 wherein thefirst and second polymeric materials are a polyether block amidecopolymer.
 10. The balloon catheter of claim 9 wherein the firstpolymeric material is a PEBAX 72D and the second polymeric material is aPEBAX 55D.
 11. The balloon catheter of claim 1 wherein the firstpolymeric material is not a lubricious polymeric material, and an innersurface of the shaft defining the guidewire lumen proximal to the tip isformed of a lubricious polymeric material.
 12. The balloon catheter ofclaim 1 wherein the second polymeric material of the tip provides asurface which has a higher tackiness than the first polymeric materialof the tip, such that the inner surface of the distal tip at least alongthe distal section thereof is not tacky at a body temperature above roomtemperature.
 13. A balloon catheter, comprising: a) an elongatedcatheter shaft having a proximal end, a distal end, a proximal shaftsection, a distal shaft section, an outer tubular member with aninflation lumen therein, and an inner tubular member with a guidewirereceiving lumen therein; b) a distal tip member located at a distal endof the catheter, having a proximal end longitudinally spaced distallyapart from a distal end of the catheter shaft inner tubular member witha gap there between, and a lumen which extends to a guidewire distalport in communication with the shaft guidewire lumen, and having aninner layer formed of a first polymeric material which has a first Shoredurometer hardness and which defines at least a section of the lumen ofthe distal tip, and an outer layer formed of a second polymeric materialwhich is of the same polymer type as the first polymeric material andwhich has a lower Shore durometer hardness than the first polymericmaterial and which is fusion bond compatible with the first polymericmaterial; and c) an inflatable balloon sealingly secured to the distalshaft section so that an interior of the balloon is in fluidcommunication with the shaft inflation lumen, formed at least in part ofa polymeric material fusion bond compatible with the first and secondpolymeric materials of the tip, and having a distal skirt section fusionbonded to a proximal end of the tip at which both the first and secondpolymeric materials of the tip are located, such that a proximal sectionof the tip is a fused blend of the balloon distal skirt section and theinner and outer layers of the tip, the fused blend having both the outerlayer material and inner layer material of the tip fused to the materialof the distal skirt section along the proximal section of the tip. 14.The balloon catheter of claim 13 wherein a lap joint secures the tip tothe balloon distal skirt section.
 15. The balloon catheter of claim 13wherein a butt joint secures the tip to the balloon distal skirtsection.
 16. A method of making a balloon catheter having an elongatedshaft with an inflation lumen and a guidewire lumen, and a balloonsealingly secured to a distal shaft section, comprising: a) positioninga proximal end of a distal tip member in contact with a distal skirtsection of the balloon, the distal tip member having coextruded innerand outer layers extending from the proximal end of the tip, and theinner layer is formed of a first polymeric material which has a firstShore durometer hardness, and the outer layer is formed of a secondpolymeric material which has a lower Shore durometer hardness than thefirst polymeric material and which is fusion bond compatible with thefirst polymeric material, and the balloon is formed at least in part ofa polymeric material fusion bond compatible with the first and secondpolymeric materials of the tip; b) applying heat and a radially inwardforce on an outer surface of a distal portion of the balloon distalskirt section to fusion bond the distal skirt section to the proximalend of the distal tip member, such that a proximal section of the bondedtip is a fused blend of the balloon distal skirt section and the innerand outer layers of the tip, the fused blend having both the outer layerand inner layer of the tip fused with the material of the distal skirtsection along the proximal section of the tip; and c) applying heat anda radially inward force on an outer surface of a proximal portion of theballoon distal skirt section, located proximal to the fusion bondeddistal tip member, to bond the distal skirt section to the elongatedshaft, such that the proximal end of the tip is longitudinally spaceddistally apart from the elongated shaft by a gap there between.
 17. Themethod of claim 16 wherein the heat applied in b) is not less than theglass transition temperature of the first polymeric material, and theheat and force are sufficient to melt the inner and outer layers of thetip along the proximal section thereof.
 18. The method of claim 16wherein the distal tip member is positioned in a) such that a distal endof the balloon distal skirt section is proximal to a distal end of thefirst layer and a distal end of the second layer of the tip.
 19. Themethod of claim 16 wherein an adhesive extends along the proximalportion and does not extend along the distal portion of the balloondistal skirt section, such that c) includes forming an adhesive bondbetween the proximal portion of the balloon distal skirt section and theshaft.
 20. The method of claim 16 wherein a) comprises positioning aproximal end of a distal tip member within a distal skirt section of theballoon, such that b) comprises fusion bonding an inner surface of thedistal skirt section to an outer surface of the tip, to form a lap jointsecuring the tip to the balloon distal skirt section.
 21. A ballooncatheter, comprising: a) an elongated catheter shaft having a proximalend, a distal end, an inflation lumen, and an inner tubular member witha guidewire receiving lumen therein; b) a distal tip member located at adistal end of the catheter, having a distal end, a proximal endlongitudinally spaced distally apart from a distal end of the cathetershaft inner tubular member with a gap there between, and a lumen whichextends to a guidewire distal port in communication with the shaftguidewire lumen, and having an inner layer formed of a first polymericmaterial which has a first Shore durometer hardness and which defines atleast a section of the lumen of the distal tip, and an outer layerformed of a second polymeric material which is of the same polymer typeas the first polymeric material and which has a lower Shore durometerhardness than the first polymeric material and which is fusion bondcompatible with the first polymeric material; and c) an inflatableballoon sealingly secured to the catheter shaft so that an interior ofthe balloon is in fluid communication with the shaft inflation lumen,formed at least in part of a polymeric material fusion bond compatiblewith the first and second polymeric materials of the tip, and having adistal skirt section with a proximal section bonded to a distal end ofthe shaft inner tubular member, and with a distal section extending to alocation distally spaced from the shaft inner tubular member having adistal end abutting and fusion bonded to the proximal end of the distaltip member at which both the first and second polymeric materials of thetip are located, such that a proximal section of the tip is a fusedblend of the balloon distal skirt section and the inner and outer layersof the distal tip, the fused blend having both the outer layer materialand inner layer material of the tip fused to the material of the distalskirt section along the proximal section of the tip, and the inner andouter layers of the tip extend along a distal section of the tip to thetip distal end.